1. Field of the Invention
The present invention relates to an image processing apparatus configured to use radiation images and visible light images and a method for the same.
2. Description of the Related Art
Existing technology in the field of radiographic X-ray equipment for medical applications facilitates visual identification of an object irradiated with X-rays by generating a combined image from an X-ray image and a video camera image.
For example, in such a method a video camera is placed at a position optically equivalent to an X-ray generation unit, and an image generated by superimposing a video camera image and an X-ray image is displayed on a monitor. The optically equivalent position refers to a set of two positions where an image captured at one of these positions is identical to an image captured at the other position. Generally, a video camera is placed at a position optically equivalent to the position where an X-ray generation unit is placed by using a half mirror.
Japanese Patent No. 3554172 discusses such a method that an X-ray generation unit and a video camera are disposed at substantially the same positions, and a combined image is generated from an X-ray image and a video camera image.
A surgical method is discussed where a surgical tool is used to puncture an object of surgery in the spinal cord after confirmation of a given position using a combined image generated from an X-ray image and a video camera image. Paracentesis, i.e., puncturing with a surgical tool, is one of less invasive surgical methods and imposes less physical burden on the patient because it requires only a smaller portion of the body to be cut out.
With this surgical method, first, an X-ray image is captured by an X-ray imaging apparatus. Then, a video camera is placed at a position that is optically equivalent to an X-ray generation unit of the X-ray imaging apparatus, and a video camera image is captured from the same angle as the X-ray image. A combined image is generated from the video camera image and the X-ray image. The surgeon locates the point of puncture by observing the combined image and marks a position on the object corresponding to the point of puncture. The puncture point thus corresponds to the marked point.
FIG. 8A illustrates a case where a successful puncture can be done in a paracentesis operation that uses a combined image generated from a video camera image and an X-ray image. A half mirror 801 transmits X-rays but reflects visible light. In the setup illustrated in FIG. 8A, an X-ray generation unit 802 and a video camera 803 are placed at positions optically equivalent to each other by using the half mirror 801 to capture an image of an object 804. X-rays emitted from the X-ray generation unit 802 pass through the object 804 and are then detected by an X-ray sensor 805.
In FIG. 8A, an X-ray 806 passes through the center of the object 804. The video camera 803 captures a video camera image of a point 808, and the X-ray sensor 805 captures an X-ray image formed from an X-ray that has passed between the point 808 and a point 809. These two captured images are then superimposed at the center of the combined image. The point 809 is located vertically below the point 808. Therefore, when the object of the paracentesis operation is located between the point 808 and the point 809, the surgical operation can be successfully carried out by marking the position of the point 808 and puncturing from the point 808 vertically downward.
An X-ray 807 illustrated in FIG. 8B passes through an edge of the object 804. As can be seen from FIG. 8B, the X-ray sensor 805 receives the X-ray 807, which has passed between a point 810 and a point 811 of the object 804, to capture an X-ray image. On the other hand, the video camera 803 captures a video camera image of the point 810.
As a result, an edge of the combined image is formed by superimposing the video camera image of the point 810 captured by the video camera 803 and the X-ray image captured by the X-ray sensor 805 from the X-ray that has passed between the point 810 and the point 811.
The point 810 and the point 811 deviate from each other by a distance d in the horizontal direction. The distance d between the corresponding points in an image generated by superimposing a visible light image, such as video camera image, and a radiation image, such as X-ray image, is hereinafter referred to as a positional deviation. When the point 811 is where punctuation is to be done, the surgical tool cannot reach the point 811 by punctuating at the point 810 vertically downward. The difficulty in the paracentesis operation becomes greater as the positional deviation d becomes larger. Thus, it is difficult to reliably locate a correct point of punctuation using a combined image.